Polymer Bulk Erosion

TLDR

Bulk‑eroding polymers exhibit a sudden mass loss after an initial lag, traditionally attributed to auto‑catalytic bulk degradation. The study develops an erosion model to test whether mechanisms beyond bulk auto‑catalysis contribute to this behavior. Using 1:1 poly(d,l‑lactic acid‑co‑glycolic acid) of varying molecular weight, the model assumes erosion starts only after degradation to water‑soluble products that contact the medium, incorporating percolation effects. Simulations show that percolation of soluble degradation products drives the spontaneous mass loss, with onset time set by degradation velocity, and the fitted rate constants agree with literature ester‑hydrolysis values, confirming the model’s validity.

Abstract

A theoretical model was developed that explains why the erosion of biodegradable bulk-eroding polymers follows the same kinetics on different time scales. poly(d,l-lactic acid-co-glycolic acid) 1:1 of various molecular weight served as a model compound. After a period of no mass loss, these polymers erode by spontaneously losing more than half of their mass, which is typical for bulk-eroding polymers in general. Until now this was explained with degradation accelerated by auto catalysis inside the bulk compared to the surface of polymer matrices. To investigate if other mechanisms might be involved as well, an erosion model was developed. It assumes that erosion can start only after the polymers are degraded to water-soluble products and after these degraded polymer areas have contact to the erosion medium. Simulations revealed that percolation phenomena may be responsible for the spontaneous mass loss and that the time of onset is a function of the degradation velocity. Degradation rate constants determined from fits to experimental data of the investigated poly(α-hydroxy esters) agree well with literature values for ester hydrolysis. This suggests that the model is in agreement with existing degradation theories.